When Is It Appropriate For Arthrodiastasis Of The First MPJ?

By Peter M. Wilusz, DPM, and Guy R. Pupp, DPM

   Applying mini-external rail fixators is relatively simple but does require some experience. Ensuring proper placement of the transcutaneous pins is important in order to facilitate proper distraction as well as adequate and correct anatomic motion during the healing process. Inaccurate placement of pins will prevent movement about the first MPJ and cause mechanical abutment of the dorsal joint surfaces. Orienting the fixator in relationship to the joint to ensure motion is key to improving outcomes. The surgeon would usually perform and confirm all of these steps under fluoroscopy.

   There are several manufacturers of small external fixators that one may use in joint distraction. In order to discuss the surgical technique, let us proceed to discuss proper mini-external fixator placement of the M-111 mini-rail (Orthofix, Inc.).

A Step-By-Step Approach To The Arthrodiastasis Procedure

   Prior to application and the appropriate osseous remodeling, one should perform joint debridement and subchondral drilling with standard closure. Be sure to inspect and mobilize the sesamoid apparatus for adhesions to the plantar aspect of the first metatarsal.

   Insert a 2 mm Kirschner wire into the head of the first metatarsal from the medial side so it is in the center of the rotation of the joint. This point is slightly dorsal of the center point of an imaginary circle outlining the first metatarsal head. Orient the fixator so the body of the fixator with the distraction mechanism is facing the proximal phalanx. The hexagon at the center of the hinge should face outward.

   Slide the articulating hinge over the Kirschner wire. Insert the 3 mm diameter bone screw through the distal seat of the distal clamp and insert the second screw into the proximal seat of the distal clamp. Manipulate the hallux, confirming that the movement is about the axis of the Kirschner wire. If not, remove and reset the Kirschner wire, adjusting the distraction mechanism as necessary.

   After confirming motion about the axis of the first metatarsal, proceed to insert the 3 mm bone screws into the distal end of the first metatarsal.

   Distract the joint 5 mm acutely (intraoperatively). Remove the Kirschner wire and tighten the articulated locking body screw. Be sure to lock the screw with the hallux in a neutral sagittal plane position.

What Does Post-Op Management Entail?

   Orthofix recommends waiting three days after surgery before begining gradual distraction. Distract the joint 0.5 mm per day until obtaining a joint space two or three times the normal width. One full clockwise turn of the threaded screw equals 1 mm of distraction.5 When the soft tissues have relaxed, loosen the articulated body locking screw to commence physical therapy. At the end of an exercise period, place the hallux in a neutral position and retighten the articulated body locking screw. Two weeks after completing the distraction, remove the fixator.

   We frequently obtain 1 cm of distraction intraoperatively, hold static distraction for seven days and then proceed to disarticulate the hinge to allow daily passive range of motion activities. We maintain the presence of distraction for four to six weeks, allowing guarded weightbearing at week one before we remove the fixator. Recently, we have performed joint distraction of the first MPJ without disarticulating the hinge for movement. We have seen excellent results postoperatively with this approach.

Case Study: When A Runner Has A Chronically Painful First MPJ

   A 63-year-old female presented for surgical consultation with a history of a painful right first metatarsophalangeal joint. She had tried multiple conservative treatment modalities over the course of 18 months without successful relief of her symptoms. The patient was an active runner and walker but could not continue to participate in these activities.

   Preoperative radiographs were significant for a dorsal medial enlargement of the metatarsal head, significant degenerative joint disease with subchondral sclerosis and widening of the first metatarsophalangeal articulation.

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